Automatic switching systems



16, 6 R. w. s. KINSEY AUTOMATIC SWITCHING SYSTEMS 4 Sheets-Sheet 2 Filed June 14, 1957 Feb. 16, 1960 R. w. s. KINSEY AUTOMATIC SWITCHING SYSTEMS Filed June 14, 1957 4 Sheets-Sheet 3 STAGE 5.

F 1 1 0 R. w. s. KINSEY 2,925,

AUTOMATIC SWITCHING SYSTEMS Filed June 14, 1957" 4 Sheets-Sheet 4 STAGEC 9+ {1 9+ 1 'STTc' 'ST ,TU I r b i 2,925,474 AUTOMATIC SWITCHING SYSTEMS Ronald William Stanley Kinsey,'West Dnlwich, London, England, assignor, by mesne assignments, toSiemens Edison Swan Limited, London, England, a company of Great Britain Application June 14, 1957, Serial No. 665,78 Claims priority, application Great Britain June 14, 1956 8 Claims. (Cl. 179-22) This invention relates to automatic selective switching systems, such as may be employed in automatic telephone exchanges, comprising a number of switching stages each afiording selective access between a number of terminal groups at one side of the stage and the same or a different number of terminal groups at the other side, which switching stages, having inter-stage connections terminating respectively on such terminal groups, such connections being hereinafter called trunksin con- 7 2,925,474 it lffit 5. 9;

.path vertical multiple providing'a number of separate paths equal to the number of contact pairs per set, while of the remaining contacts'correspondingcontacts from the several sets in each horizontal row are also'electrically interconnected to constitute a multi-path horizontal mul-' tiple. The arrangement thus provides that any one ofa number of terminal groups (for example ten or twenty) connected respectively to the multi-path vertical multiples can be given access to' any one of a number formity with telephone terminology, are controlled by respective control circuits each ot;which-, in response to receipt of a setting signal identifying a t'runkterminating at one side of the appertaining stage and selected other than by the control circuit in question, fulfills the follow x ing functions, namely: selects a-free trunk terminating at the other side of the-stage and extending to the next stage, if any; controls the establishment of a circuit through the stage between the selected trunks at its opposite sides; and effects the transmission to "suchsnext, stage of a setting signal relative to the selected inter-V stage trunk thereto. Such switching systems will hereinafter be referred to as being, of the kind. specified.

The invention has animportant application in and will be described with particular reference to ,a semi-elec-' tronic system employing electromechanical selector switches of the cross-bar type (or equivalent switching arrangements) controlled by devices of .an electronic nature such as thermionic or;cold-cathode valves or transistors. It is to be-understood, however, that the invention is also applicable to fully electronic systems, in which for example theswitches are constituted by electronic devices such as cold-cathode valves or transistors, and to otherv systems employing for instance motor uniselector switches. Y

Before going on to describe the invention, it is thought to be desirable to indicate in general terms'some con- 'siderations involved in providing a' cross-bar sw tching,

stage in an automatic switching system {A cross-bar switch unit, an example of which will be found described in volume 2 at pages 639-640, of the text-book Telephony, by J. Atkinson, essentially consists in its usual;

form of an assembly of contact sets (each comprising a number of co-operating hired and moving contacts) which are arranged matrix-wise in a number of'horizontalancl vertical rows of which there are usually -ten horizontal rows and ten or twenty vertical rows. These of terminal groups (forexample ten) connected respectively to the horizontal multiples, it being appreciated that the terminals of each group are connected respec.-' tively to the several paths afforded by the multiple t which the group as a whole is connected.

A cross-bar switch may comprise a single crossbar unit or, if desired, a number of cross-bar unitsopr ating in conjunction to cater for a difierent number of terminal groups, and thus if possible connections thereto, on either side of the switch; for instance ten crossbar units having ten vertical contact rows each, or five cross-bar units having twenty vertical rows each, providing a hundred vertical multiples in either case, may have their horizontal selecting bars arranged to operate together and the horizontal multipling continued through all the units to provide a composite switch'through which each of a hundred terminal groups connected to the vertical multiples has access to-tenterniinal groups connectedto the horizontal multiples. 7

In an exchange system of-th'e kind above specified any- 7 switching stage may therefore comprise {plurality of cross-bar switches together providing access between a' number'of terminal groups which on ohe orjeach side" of the stage isgreater than could conveniently be catered for by: a single switch. Thus for example a switching contact sets areselectively actuable by the operation of electromagnets provided one for each vertical row (hold magnets) and one for each horizontalrrow (select magnets), the operation of a select magnet and a hold magnet, in that order, causing operation of a horizontal selecting member and vertical holding member which together are efiective to actuate the contact set at the cross-point of the horizontal and vertical" rows to which the operated magnets respectively pertain; Contacts corresponding to'ea'ch other in the several sets I in each vertical row, one contact from each co-operating pair, are electrically interconnectedto constitutea multi corded information the setting of the switches'of the -stage appropriatelyto establishing a through-connectio'rrj-i In tl'te telephone exchange system described in said' stage employing single-unit "cross-bar switches may coinprise ten primary switches having their horizontal.

multiples cross-linked with' 'those {of ten secondary switches, so as, assuming ten vertical 'm'ultiples percrossbar unit,'to afiord selective accessbetween, for example, a hundred trunks connectedto the vertical multipleso'f the primary switches by way of 'the respective terminal groups and a hundred trunks likewise connected to the verticalmultiples of the secondary switches, the term' trunk as used herein denoting an inter-stage connection as distinct from a connection, called a link, between switches within one and the same stage. The numbers mentioned may be multiplied by employing for a switching stage a number of what will be termed frames each comprising a plurality of primary and secondary'switches" cross-linked in the frames. Y

In a switching systemof the kind specified employing" electronically controlled cross-bar switches, a forward markedpath availablefor the extension of "a call forwards from a' calling .subscribers line to a register, 'likewise a backward-marked path available for the 'exten sion of the call towards the called subscriber.s line, may

at each switching stage involved be appropriated for the call by electronic means included in the control circuit? for the stage, which electronicm'eans, in responseto a setting signal reverted from stage to stageftowards a calling or called subscriber in consequencelof 'thefor? ward orbackward'markingas the case may be, is efiee'- tive to recordthe identities of the inter stagetrunks which are includedin said path at the opposite sides of, the stage concerned, and also" of any intermediate linkin the stage, and to control in accordance-with there between said' trunks: an exchange system operating broadly onthese lines forms'the' subject'of our applica-f tion No. 472,727.

application, in which each cross-bar switching stage (or link-frame as it is termed therein) comprises a plurality of primary and secondary cross-bar switches cross-linked on their horizontal multiples and having the inter-stage trunks on opposite sides of the stage connected to the vertical multiples, the setting signal received by the control circuit for any switching stage fully identifies a particular trunk at one side of the stage. Considering any particular stage whose control circuit will receive its setting signal from an adjacent switching stage that has selected a free and marked inter-stage trunk, the setting signal therefore identifying this trunk, the control circuit at the stage considered responds to the setting signal to record in a first electronic store the identity of the switch (on one side of the stage) to which that trunk identified by the signal is connected, to record in a second electronic store the position in that switch at which the trunk is connected to select and record in an electronic store the identity of a switch (on the other side of the stage) having a free and marked link between it and said switch on the first side, and to select and record in a fourth electronic store the identity of a free and marked trunk connected to the selected switch on the second side, the control circuit being effective, in accordance with the information stored, to operate the appropriate select and hold magnets for establishing throughthe relevant crossbar switches and over said free link a through-connection betwe'en the free trunks concerned.

T he present invention, which is especially applicable to a telephone exchange system such as that described in our said copending application and when so applied can result in a significant reduction in the amount of equipment required, is based on the realisation that to fulfill its function the control circuit of a multi-switch stage requires to know only the identity of the switch to which an externally selected trunk is connected and thatfwhere such trunk is an inter-stage one selected by another switching stage, the identity of the trunk is already known by this latter circuit.

This prior knowledge arises from the fact that in a cross-bar system any trunk between two stages must be connected at its opposite ends to particular horizontal multiples or more usually to particular vertical multiples, in respective switches of the stages; the positions of the multiples concerned in their switches, and likewise the position of the switches in the stages, are not necessarily the same andin fact are usually so chose as to give each switch in one stage access to all the switches in the other stage through respective-inter-stage trunks; For setting. up a through-connection over any inter-stage trunk between the two stages it is therefore necessary, inter alia, to eifect' operation of the cross-bar magnets (select or hold as the case maybe) relating re spectively to those multiples to which the opposite ends of the inter-stage trunk are connected in the two stages. According to the present invention therefore, in a selective switching system including first and second crossbar switchingstages, the magnets pertaining as indicated above to opposite ends of any particular trunk extending between the first and second stages are electrically coupled so as to be energised contemporaneously by a control circuit for the first stage following selection by the 1atter of that trunk. A control circuit for the second stage can then be arranged, in response to the setting signal identifying the switch to which the inter-stage trunk is connected, to cause selective energisation in that. switch of the transversely operating magnet appropriate to establishing by way of the switch the selectedthrough-connection above referred to: that is, if the inter-stage trunks are connected, say, to the vertical multiples in the second stage then the hold magnets relating to these vertical multiples in the relevant switches will be'couple'd in the manner indicated for energisation by the first stage control circuit, while the select magnets relating: toathe; horizontal, multiples inthe same switches are arranged for selective energisation by the second stage control circuit.

In this way the amount of equipment in the control circuit of the second stage can be appreciably reduced since this circuit no longer takes part in storing the identity of the inter-stage trunk. Thus as compared with the electronic control circuit requirements of the exchange system of our said copending application, each control circuit for a second switching stage of an adjacent pair would require one less electronic store and a corresponding reduction in the number of components required for coupling the stores to the cross-bar switch magnets for operating the latter, this being achieved with the addition of a pair of inter-stage trunk wires coupling the magnets pertaining to the opposite ends of the trunk, or possibly, as indicated later, over an existing P-wire in the trunk. Moreover, since the number of switches involved is less than the total number of interstage trunks the requirements for signalling on a switch basis in accordance with the invention are less than for signalling on a trunk basis: for instance if there were ten inter-stage trunks leading to each of a hundred switches in a stage, the setting signal would only have to identify one out of a hundred switches as against one out of a thousand trunks.

In describing by way of illustrative example a particular embodiment of the invention as applied to an electronically controlled cross-bar exchange, reference will be made to the accompanying drawings in which:

Fig. 1 is an abbreviated schematic trunking diagram illustrating for an intermediate switching stage comprising primary and secondary side cross-bar switches; the cross-linking between these switches on their horizontal multiples and the cross-connection of their vertical multiples with adjacent similar stages on each side;

Figs. 2a, 2b and 2c, when placed together left-to-right in that order, constitute an abbreviated illustration showing the essential features, so far as regards the invention, of the embodiment to be described; and

Fig.3 illustrates the mode of interconnecting the operating magnets of the cross-bar switches.

Referring to Fig. 1 the dotted rectangles FA, PB and FC represent one frame each of respective switching stages A, B and C. The frame FB of stage B comprises ten primary cross-bar switches P1 P10 and ten secondary cross-bar switches S1 S10, only two of the primary switches and two of the secondary switches being represented. The frames FA and PC of stages A and C are each similar to frame FB, only the secondary switches S1 S10 of frame FA and the primary switches P1 P10 of frame FC being represented.

I Each cross-bar switch is assumed to have ten vertical multiples, represented by the vertical lines V, which in the manner previously described have selective access through the switch with ten horizontal multiples represented by thehorizontal lines H. In eachframe the horizontal multiples of the primaryand secondary switches are crosslinked in such manner that each primary switch P in the frame has a link to each secondary switch'S therein. Some typical links are represented at LK for frame EB of stage B. Vertical multiples of the secondary switches S t of frame FA of stage A are cross-connected with vertical multiples of theprimary switches P of frame FB of stage B; these cross-connections'being typically, represented at T1. Other vertical multiplesof the secondary switches S in frame FA may be likewise cross-connected with vertical multiples in primary, switches of other frames (not shown) in stage B. In the same manner, vertical mul' tiplesof the secondary switches ,S of frame FB of stage B are cross-connected, by trunks-typified by T2, with verticalmultiples ofth'e primary switches in frame PC of stage A- and possibly also other frames of this latter stage. Sincethere' areiten switches in each frame and ten vertical mul-- tiples-per switch therewill be a total of a hundred trunks extending; from each frame to the adjacent stage. The

vertical multiples of theprimary switches (not shown) of stage A and of the secondary switches (also not shown) of stage C may have connected to them, dependent on the position and function of thesestages in the overall exchange, either trunks leading to other switching stages or connections leading for instance to subscribers lines. Each frame has its own control circuit, the portions of whichrelevant to the present invention will now be described with reference to Figs. 2a, 2b and 2c laid together in the manner indicated.

Referring thereto, there is shown in respect of stage B, for one frame of that stage, a representation of one primary switch PB and one secondary switch 'SBof the frame together with a single link LK extending between horizontal multiples of these switches, each link being assumed to include the so-called and P-wires commonly found in an automatic telephone exchange. The operating (select) magnets associated with the horizontal multiples to which the opposite ends of the link LK are connected in the switches PB and SB respectively are indicated at SMP for the primary switch and SMS for the secondary switch. A single trunk T1 isshown connecting one of the vertical multiples of the. switch PB in stage B to one of the vertical multiples of a secondary switch SA in stage A, this trunk being representative of all the trunks (a hundred per frame in total) interconnecting the primaryswitches PBof stage 13' with the secondary switches, of which SA is typical, of stage A.

tubes such as MTSb, and those such as MTPb respec tively.

In a manner analogous to that which will be described later for the'tubes such as MTSb, the markingsignal as extended over the control circuit FCA for frame FA of stage A will fire those of the tubes such as MTSa which relate to secondary switches such as SA of this frame having appropriate free links extending to them from the primary side (not shown) of theframe. The marking is thereupon extended towards the frame control circuits for stage B from the cathode of each tube such as MTSa thus fired, it being appreciated that the firing of such tube will by reason of its cathode resistor such as 11, cause its cathode potential to be raised to a marking value. Assumingtube MTSa relating to switch SA is fired and considering the extension of the marking from its cathode, it is required that this marking should indicate which of the ten trunks such as T1 leading'to stage such as MTSa to ten tubes. such as MTPb, and in order The operating (hold) magnets associated with the vertical multiples to which the opposite ends of the trunk T1 are connected, are indicated at'HSA and HPB at stages A and B respectively. The trunk. T1 includes (e) ands P-wires connecting between the switches as indicated, and also two additional wires m1 and m2 connectingthe hold magnets HSA and HPB in parallel. A similar typical trunk T2 is shown connecting one of the vertical multiples of secondary switch SB in stage .B with one of the vertical multiples. of a primary switch -PC of' stage C, the hold magnets HSB and HPC relating to these vertical multiples being connected in parallel over the m wires'in this trunk. I

The figures under consideration also illustrate in an abbreviated manner, relevant portions of frame control circuits FCA, PCB and FCC for the represented frames FA, PB and PC of stages A, B and C respectively.

Conforming to the requirements 'of an exchange such as that described for instance in our said copending application or in our application No. 665,774 it will be assumed that in the operation of an exchange embodying the switching stages A, B and C, a marking signal is extended over the control circuits such as FCA, PCB and FCC of the various stages, indicating in the process what trunks such as T1 and T2 and what links such as LK are free for inclusion of a through-connection through the stages, and that a setting signal reverted over the control circuits from stage to stage controls the selection and tubes relating one to each of the ten secondary switches.

such as SA in frame PA of stage A. The control circuit FCBis shown as including cold-cathode discharge tubes MTPb and MTSb each typical of ten such tubes respectively relating in the one case to the ten primary switches.

such'as PB in frame FB of stage B and in the other case to the ten secondary switches SB of that frame. The control circuit FCC includes a cold-cathodedischarge tube MTPc typifying ten such tubes relating oneto each of the ten primary switches such as PC in frame to minimise the amount of cabling required between the frame control .circuits'of the successive stages, tubes such asDTl, one for each tube such. asMTSa, are provided in physical locations relatively near, the stage -B andits frame control circuits. A marking at the cathode of a tube such as MTSa appears at the trigger electrode of the correspondingtube DT1 and thereby fires this latter tube, causing a marking to appear at its cathode. This marking is extended, over a common cml, to ten paths )1 leading to the trigger electrodes of those tentubes such as MTPb which relate as previously indicated to the switches PB having trunks such as T1 extending to them from the switch SA represented by the fired tube such as MTSa.

Since each of the switches such as PB has ten trunks such as ,T1 leading to it from respective switches such as SA in stage A, the trigger electrode of each tube such as MTPb will have ten paths such as p1 leading to it from different tubes suchas DTl, this being indicated by the common cm2. The total number of paths such as p1, will therefore be equal to the number of trunks such as T1 between stages A and B,-each path relating to its own particular trunk.

Each path such as p1 includes an isolating rectifier such as R1! and a contact, such as acl, which is an auxiliary contact controlled by the hold magnet such as HPB associated with the vertical multiple to which the trunk represented by the path concerned 'is connected in a switch such as PB. Each contact such as acl is normally closed 'butris open when the magnet controlling it is energised, namely when the switch such as PB with which that magnet is associated has been set to establish a connection'through it between the trunk such as T1 and a link such as LK. Thus if a trunk such as T1 is already engaged in an established through-connection, the contact such as acl in the corresponding path such as p1 will be open. I

A marking initiated by the firingof any tube such as MTSa relating to a particular secondary switch such as SA in stage A, will therefore be extended, by way of a PC of stage C. The tubes such as MTSa and-those such Y .as MTPc are assumed to be connected in the same mannet as, and therefore to be controlledsirnilarly to, the

tube such as DTl, over the associated paths'such as p1 in which the contacts acl are still closed. This results in the firing of those tubes such'as MT Pb which relate to primary switches such as PB in stage B having free trunks extending to them from the particular secondary switch concerned in stage A. v V Considering any tube such as MTPb thus fired in the.

control circuit FCB for frame FB, the tube provides'at its cathode a marking which is applied in commo nas aces-4st ineieated at 6M3, to ten paths such as p2 leading respectively to the trigger electrode of the ten tubes such MTSb relating to the secondary switches such as SB that frame. These ten paths respectively correspond t6 the ten links such as LK which extend to these secondary switches from the primary switch such as PB to which the MTPb tube being considered relates. Since each switch such as SB in frame FB has a link extending to it from each primary switch such as PB in the frame, the trigger electrode of each tube such as MTSb in the frame control circuit FCB has paths such as p2 leading to it from the cathodes of all the tubes such as MTPb in that circuit (common c1124).

Each of the paths such as p2 includes, in series, a resistor such as r2 and a rectifier such as Rf2 the junction point of which is connected via a rectifier in a lead such as x to the P-wire in the link such as LK to which the path corresponds. It is assumed that, in conformity with practice, a holding earth is applied over the P-wires of the trunks such as T1 and T2 included in an established through-connection, this holding earth being extended through the switching stages over the P-wires in the frame links such as LK included in the connection. Thus if a link is busy its P-wire will be earthed. Consequently a marking appearing from a fired tube such as MTPb on a path such as p2 corresponding to a busy link such as LK, will be diverted to earth. The marking applied to a path such as p2 corresponding to a free link, however, will be extended over. the path to fire the relevant tube such as MTSb relating to the secondary switch such as SE to which that link extends.

From the cathode of any tube such as MTSb thus fired, a marking is extended, by way of a corresponding tube such as DTZ, at the common cmS ten paths such as p3 corresponding respectively to those trunks such as T2 which extend between the stage B secondary switch to which the fired MTSb tube relates and respective primary switches such as PC in stage C. These paths such as p3 lead respectively to the trigger electrodes of the tubes such as MTPc relating to the stage C primary switches such as PC to which the corresponding T2 trunks extend, each path including a ccntact such as ac2 which is controlled, in a manner similar to that already described for the contacts such as acl, by the hold magnets associated with the vertical multiples to which the corresponding T2 trunks are connected in the stage C primary switches. The extension of the marking to stage C following the firing of a tube such as MTSb, corresponds in all respects to the already described extension of the marking to stage B following the firing of a tube such as MTSa- A markinghaving been extended through. all switching stages to indicate in the manner described all appropriate trunks and links available for inclusion in a through-connection through the stages, a setting signal is reverted in response to which the frame control circuits select and effectively record the identities of certain of.

these trunks and links for subsequent inclusion in a through-circuit established by appropriately setting the relevant switches in the several stages.

Let it be assumed that in response to the reverted setting signal the frame control circuit FCC for frame PC in stage C has selected, in a manner similar to that which will be described later for the control circuit PCB of stage B, a particular trunk such as T2 which, extend-- ing between a secondary switch such as SB in stage B and a primary switch such as PC in stage C, had been indicated by the marking process as being ree. By firing one of ten cold-cathode tubes typified by STPc, the con trol circuit FCC records the identity of the primary switch such as PC to which the selected trunk is connected in stage C. It also records, by firing one of ten celdcathode tubes typified by S'l'Tc, which one of theten trunks connected to the recorded switch such as PC isthe one selected; The cathodes of the tubes such as STP- are respectively 'c neeted te tenleads such as 17 which relate one to each primary switch in frame PC of stage C. Likewise the cathodes of the tubes such as STTC are connected respectively to ten leads such as 18 which relate to the ditferentvertical multiples in any primary switch of the frame.

Each of the leads such as 17 is paired individually with each of the leads such as 18, and each pair is com n'ccted through a resistance-rectifier gating circuit such as that constituted by r3, Rf3 and Rf4 to an individual point such as P1. For each frame of stage C there are therefore a hundred points such as Pl: these relate respectively to the hundred trunks leading to stage B from the relevant frame. With a particular primary switch of stage C selected and recorded by the firing of one of the STPc tubes, and with a particular trunk con nested to that switch selected and recorded by the firing of one of the STTc tubes, the consequent rise in potential at the cathodes of the fired tubes becomes applied by the action of the gate pairing these cathodes to mark the particular point such as P1 pertaining to the selected trunk.

Of the points such as' Pl, all those relating to trunks which lead to the secondary switch such as SB in stage B are connected in common, as indicated at cmd, to the trigger electrode of a cold-cathode tube such as DT3, there being one such tube for each secondary switch in stage B. Thus following selection of a particular trunk, the marking applied at the corresponding point such as Fl fires the tube such as DT3 relating to the secondary switch of stage B to which the trunk extends. The marking then appearing at the cathode of the fired DT3 tubes is transmitted as a setting signal to the relevant frame control circuit of stage B over a signalling wire such as 19, there being one such wire per secondary switch in stage B.

Assume that at stage B the frame control circuit PCB receives a setting signal over lead 19 to indicate that the trunk selected and recorded at stage C leads to switch SE in frame PB of stage B. This setting signal is applied in common, as indicated at 01217, to ten paths p4 leading to the trigger electrodes of respective cold-cathode tubes typified by the tube TPb. As indicated at cm8, each of the tubes such as TPb has its trigger electrode also connected, over paths similar to p4, to the cathodes of the other tubes such as DT3 relating to the other switches such as SB in frame PB of stage B. The paths such as p4, each comprising a resistance such as rdin series with a rectifier such as Rf5, can therefore be considered as representing respectively all the links such as LK between the primary and secondary switches of frame FB.

From the junction of the resistance and rectifier in each path such as p4, a test lead T11 extends via-a rectifiersuch as Rffi and lead x to the P-wire of the related link such as LK. It also extends via a rectifier such as Rf? and resistance r to the cathode of the tube MTPb relating to the primary switch such as PB to which that link is connected. If the link is busy or if the cathode of the MT?!) tube is unmarked, any marking on the path such as p4 in question will be diverted to earth over its test link such as T11. Otherwise such marking will firethe TPb tube to which the path extends. Thus of the ten TPb tubes in the frame control circuit PCB, those tubes will be fired which relate to primary switches having free and effectively marked links such as LK extending from them to the secondary switch S3 identified by the fired DT3 tube as having the selected trunk connected to it.

Toselec't one of the possible plurality of fired T'Ph tubes and thereby select one of the primary switches just referred to, a one-only selection circuit including a Dekatron multi-cathc-de cold-cathode tube D1 is em ployed. Briefly this t'ub'e D1, which is represented in conventional symbolic-term, comprises in an evacuated {the stage 'C frame FC..

envelope an anode a'surrounded by ten circumferentially distributed cathodes 1 10. The tube is kept alive 7 Theten TPb tubes in the control circuit FCB for frame 'FB are respectively associatedwith the cathodes of the tube D1 by having their anodes connected to the relevant cathodes through the winding such as W1 of a saturable reactor such as SA1,rthere being one such saturable reactor for each Dekatron cathode. When any TPb tube is fired, the resultant drop in its anode potential is therefore transmitted to the associated Dekatron cathode, resulting in this cathode tending to take over the discharge in the tube D1. Should more than one Tlbtubef have been fired, indicating that links such as LK areavailable to more than one primary switch in the frame, only one of the associated cathodes will take the discharge" and the others will be elfectively locked out in consequence of the resultant voltage drop across-the anode resistor r5 of the tube D1, There is thus an eifective one-only selection by which one-of the available-pri- T pertinenfito the trunk concerned. This latter tube iwill therefore be fired; For any other free trunks such as T2, namely trunks connected to primary switches of stage B other than the one selected, the STPb tubesrelating to these primary switches will not have been fired and their. cathodes will therefore be near earth potential. Consequently a marking on a related test lead suchas iTlZ would be'div'erted to earthby way of the rectifier such as Rf8 in the p path concerned, thus preventing such marking from firing a TTb tube.

Since there may be more than one free trunk available to stage A from the selected primary switch of stage mary switches is preferentially selectedby its associated cathode in the Dekatron taking the discharge. 7

The particular a primary switch thus selected-is recorded by'the firing of a tube suehas STPb in conse-v w-quence of the current flow at the Dekatron cathode then taking the discharge: this current flow passes through vrthe control winding such as .Wl of the associatedsaturable I reactor such as SAl, resulting-in this reactor'producing ,1

'a'noutput signal which, after .rectification'in -'a"volt age doubling circuit such as'RFI, is applied to the relevant :tubeSTPb to fire it. It will be appreciated that there is one ;such STPb tube for each primary switch in the frame F13 and that they correspond to'the't'ubes suchas STPc alreadyreferred to in the control circuit-FCC for Having thus 'in effect selectediin stage B a particular primary switch having a free link to'the' secondary as' l'f and; Z8, these leads such a's1 l 7' and l8 are connected Y B, more than one of the TTbtubes may be fired in the manner indicated. To select a particular one of these trunks, a one-only selection circuit is employed which includes a Dekatron D2 and is similar in constitution and operation to the previously described one-only selection .circuit including Dekatron Dl. Asbefore; the current how at the cathode which takes the discharge in Dekatron D2 when a selection action takes place, passes through the control winding such as W2 of a saturable reactor such as SA2 and causes this reactor to produce an output which, after'rectifi'cation in a voltage doubling circuit such as RF2,,fires an associated tube such as'S TTb (which :isone of ten)qtotrecord which, trunk such as T1 has been selected from thoseconnected to the previously selected stage B primary switch such as PB,f The'tubes1suc h as .STTb correspondfor stage B torthosesuch as STTc already referred to for stage C. Y e

The tubessuch as VSTPb relat ng to respective primary sw itchesin'- frame ,FB-of stage B, and likewise the-tubes i such as STTIz'rrelating-to respectivetrunks such as T1 se; switchesghave leads suchggas l7 and' c onnected;to ,their cathodes. In a rnanfner similar to that previously described for the leads such pairs, through resistance-rectifier gates .such as. that constituted by resistance r1 and i'rectifiers Rflt) and Rfll, V to individual points such as P2 relating respectively to all ,the trunks such as T1 leading tostage A from frame FB of stage B. Thus with one of the STPb tubes andone switch to which the selected trunk from stage C is-connected,it is now required to select a particular free and marked trunk leading to stage A from that primary switch of stage B. To this end; eachof'the tubes such as :STPbhas its cathode connected intcomrnon, asin dicat ed at cm9, over respective paths such as p5 to the respectively the ten trunks,.leadingito stage.:A-Jfrom any a trigger. electrodes. of ten tub'esfsuch as TTb representing? primary'switch of stage'B. '.;Eacli.of-the- TTb tubes has its trigger electrode connected vover similar paths mine cathodes of the other STPb tubes also; as indicatedby V the common emit), so, that there .will be a IOIalLTOf-QL hundred paths such as p5 relating respectively to all the ;A a nd B.:. t i e t .,Thetenpoints such as P2 relating to trunks such as T1 leadingfto the sarnevsecond ary. switch in stage A arecon nectediover acornmoncnill as before to the irigge'r elec iof th e STTb tubes fired, one ofwthepoints such as P2 will be marked from the Cathodeslof these tubes to indi- Zcate the particular trunk. selected between the stages pass or "aitube such as 1DT4 relatingjindividually' to that switch; Thl lS' on selection at stage B of aparticular'trunk such as T1 fleading'to" stage A; one' of'the tubes suchas will bel fired in the same manner as described for tube D T3, td indicate the particular'secondary switch to trunks extending to stageA fromframeF B ofstageB;

Each of the'paths such as p5'compris'e s two oppositely poled rectifiers such as 'R S and Rf9. inj seriesl jFrom the junction of these 'rectifiersjin eachpath, a test lea d ,suchz.:

as T12 extends over a resistor such as 16 tofthe path such as p1 relating to the'same'trunk, beingconnected .to the latter path on the opposite side of the contact such as,

acl therein from the tube such asDT-l. -If .theit'runk to which a particular p5 path relates is'fr'ee;(ac1 .contacts provide power amplification for driving the setting signals .overfthe leads 'such as and 'l9 to stages B and A closed) and if thecorresponding p1 path has been marked by thefiring of a DT.1.tube, the relevant test lead such as Tl2 :will takeia relatively positive markingpotential to the junction of the rectifiers such as R18 and Rj9 in", V

' the p5 path in question- If this trunk is one that. is con;

nected' tothe selected primary switch, the STPb tube" to a the cathode of which this latter path .is1conncted will have been fired; the resultant raised potential'at its oath-.

which.that trnnkis tconnected in stage B, :a corresponding setting signal being transmitted to the relevantfrarne con;

trol'circ iit: of'stage A over: a signal lead such as [59' eon- V nected tojthe cathode of the fired DT4 tube. 1 At stage' A,y

such as FCA, including tubes such a s TPa correspgi1d+ ing 'to the tubes such as TPb at stage B, performs" a 7 similar; recording and selecting function to that described ior stage B. V 1 e r .The tubes "such as DTS and DT4 are preferably llr a ez rted physically nearthe stages C and B respectively andin addition to acting as stora'ge tubes may then also respectively j v r I Once the selection of trunks'and links for inclusion tion stored by the control-circuits. Considering stagetB;

fiertsuchaszRfQzto the{trigger.electrode ofthejll'lbitube lnsince zeachplink such as"LK*-extends .between particular in .responseto this'setnng signal, the framecontrol circuit 11 P y d se o d y he and s nce the oppo ite .ends of such link are connected to particular horizontal multiples in these switches, then once a particular link has been selected its subsequent inclusion in the throughconnection established through the switching stages can be effected by energising together the operating '(select) magnets relating to these horizontal multiples in t e two switches. The magnets may therefore be permanently coupled together as exemplified in Fig. 2b by the parallel connection of typical select magnets SMP and SMS relating in the manner indicated to opposite ends of the link LK between the switches PB and SB. Likewise since the opposite ends of each trunk such as T1 are respectively connected to particular vertical multiples in a primary switch of stage B and a secondary switch of stage A, the operating (hold) magnets associated with these particular vertical multiples can be coupled together: thus by way of an example typical of all the trunks such as T1, the hold magnets HSA and HPB, relating to the vertical multiples to which the trunk T1 is connected in switches SA and PB, have been shown connected together in parallel. The same applies for each trunk such as T2 between stages P and C, the hold magnets such as HSB and HPC relating to vertical multiples to which opposite e'nds of such trunk are connected, being likewise connected in parallel as shown.

The identities of the stage B primary and secondary switches between which a selected link such as LK is connected, are recorded by the fired conditions of one of the STPb tubes and one of the DT3 tubes respectively a as has been previously explained.- The information stored by these fired tubes, considered" together, therefore. identifies the selected-link. Consequently for setting the switches to include the selected link in a throughconnection, control signals taken from the cathodes of these tubes over leads such as a and b respectively, can be used to energise the coupled select magnets such as SMP and SMS relating to the selected link.

The identity of v a selected trunk such as T1 between stages B and A is recorded by the fired conditions, considered together, of one of the STPb tubes and one of the STTb tubes as previously indicated. Consequently for setting the switches to include the selected trunk in a through-connection, control signals taken from the cathodes of these tubes over leads such as b and '0 respectively can be used to energise the coupled' hold magnets such as HPB and HSA relating tothe selected.

The. same applies in respect to a selected trunk trunk. such as T2 between stages-B and C, in which case the coupled hold magnets such as H53 and HPC relating to the trunk can be energised by control signals taken from cathodes of the fired STPc and STTc tubes over leads'such as b' and c. r a The select and hold magnets of the switches in any frame maybe connected, for control by the signals derived over the leads such as'a, b and c, .in' the manner now to be described for a single frame ofstage B with reference to Fig. 3, similar magnet connections, being assumed for the switches in other frames and .other stages.

Referring to Fig. 3, the illustration is abbreviated by representing only two of the vertical hold magnets V1 and V for each of only two of the primary switches P1 and P10 and for each of only twoof the secondary. switches S1 and S10. 1 Also, the horizontal select magnets pertaining to only four links between the primary and secondary switches have been represented, these links having been respectively assumed to extend between *the first horizontals of switches PPl and S1 (magnet H1 in each switch), between the tenth horizontals of switches P10 and S10 (magnet H10 in each switch), between the first horizontal of switch P1 and thetenth horizontal of switchs'lti (magnets'l l'l and H10 respectively), and

between the tenth horizontal of switch P1 and the first horizontal oi switch P10 (magnets H10 a d 1-11 respectively); these therefore conform to the links LK actually illustrated in Fig. 1. Each magnet is represented in Fig. 3 by a correspondingly labelled rectangle at the .side of which is appended the switch reference corresponding to the switch to which the magnet belongs.

In Fig. 3 the top row of rectangles includes the hold magnets belonging to primary switch P1 and the coupled horizontal magnets relating to the two links connected to that switch. The bottom row includes the hold magnets belonging to primary switch P10 and the coupled horizontal magnets relating to the two links connected to this latter switch. Considering only these magnets (that is, ignoring for the moment the hold magnets of the secondary switches S1 and S10), those in the top row are connected on one side in common, through isolating rectifiers Rf, to the anode of an earthed cathode discharge tube VT]. the trigger electrode of which is .cou pled at terminal B1, over one of the b leads (Fig. 2b) to the cathode of the STPb tube relating to the primary switch P1. Likewise the magnets being considered in 1-1 6 bottom row are connected on one side, also through isolating rectifiers R to the anode of a similar tube VTlO the trigger electrode of which is coupled at :terminal' B19, over another of the b leads to the cathode of the STPb tube relating to the primary switch P10. Magnets similarly associated with each other primary switch are likewise connected via terminals corresponding to B1 and Bid to tubes similar .to VT1 and VT10 and having their trigger: electrodes appropriately .connected to theremaining b leads. I

The other sides of the vertical magnets V1 in all the primary-switches P1 P10 are connected in common to terminal C1 and from there are coupled, over one .of the c leads- (Fig. 2a), to the cathode of the STTb tube which relates to the particular trunk connections (vertical multiples) to which the V1 magnets relate. Likewise the V10 vertical magnets are cornmoned to terminal C10 and connected over a 0 lead to the cathode of the relevant STTb tube. The other vertical magnets in the primary switches are likewise grouped and connected in each group with the relevant STlb tube. Each vertical magnet, being related to one end of a particular trunk, is connected in parallel as previously described, to the vertical magnet which likewise relates, in a secondary switch of stage A, to the other end of the same trunk. This parallel connectionis indicated by the lines such as mil and'mZ.

The coupled horizontal select magnets relating to each link extending to the secondary switch S1 are connected in common, on 7 their other sides from the tubes VTI VT10, to terminal A1 coupled over one of the a leads (Fig. 20) to the cathode of the DT3 tube relating to switch S1. 'Of the horizontal magnets shown, those connected in this way are the magnet H1 of switch P1 coupled with magnet H1 of switch S1, and the magnet H1 of switch Pit) coupled with magnetI-Illl of switch S1. Likewise the remaining horizontal magnets shown,

I relating to links extending to the secondary switch S10,

are connected incommon to terminal A10 coupled over another of the a leads to the cathode of the DT3 tube pertaining to switch 810. 7 The select magnets similarly related to each other secondary switch are likewise connected, via terminals corresponding to A1 and A10, to the relevant DT3 tube. The hold magnets Vi V10 of the secondary switches S1 S1tl'are coupled for cnergisation in parallel with corresponding hold "magnets of the primary switches "in stage C as previously described, the parallel connection'being again indicated by the dotted lines such as m1 and m2 attached to these magnets in Fig. '3.

The "coupling'between each a, b and 0 lead and-the corresponding A, B and C terminals includes suitable inhibiting means (not shown) by which a-signal appear.- ing on any of these leads on firing of 1 the associated 13 storage tube is prevented from reaching theterminal concerned until the selecting and recordingfunction-has stage :tostage as each stage is set in succession, it is contemplated that instead of employing separate in wires been completed in all the switching stages,'-this being i necessary to enable provision to be made for-theproper order of operation of the select'and hold magnets in each switch concerned. After the control circuits have all been set, at which time one a lead, one b lead and one 0 lead will be carryingasignal in thefranie control circuit FCB (Figs. 2a2c)-of stage B, the inhibitions are removed andthese signals appear at the corresponding A, B and C terminals of 3. By virtue of-the interconnection of the magnets as described in relation to this latter figure, these signals are then combined 'to "for connecting the coupled hold magnets, the coupling inlay be effectedoverjthe P-wire in the trunk with which the magnets are associated,this being done byconnectingv the operating winding of each of the two magnets (in stead ofth'erholding windings thereof as shown) between the P-wire :and an appropriate source of potential so that when earth is applied to the 'P-wire in consequence for instance of theenergised select magnet in a preceding stage closing auxiliaryicontacts between earth and the ill-wire, enrgisingzcurrenttor themagnets flows between iearthiand said source; It is also possible that instead of energise the select magnets such. as SM'P'afid SMS which:

relate to opposite ends of the selected link such asj LK in Fig. 2b,and also 'to'energise the hold magnet such as HPB' which relates, in the stage B primaryswitch to.

' inclusion in the through-connectiontoj be established, a linlg such as LK connected between the first horizontal m lt es of t h s P ndfs f S es B (t W -h S1, ha n con c to it the twi l? h va T2 Slt by a frame control circuit of stage C),land a trunk such as T1 connected to the first vertical multiple of P1. The identity of the secondary switch1S 1 concerned is recorded by the fired condition of the relevant one of the DT3 tubes; the identityof the primary switch P1- concerned is recorded by the fired condition of the relevant one of the S TPb tubes; and the vertieal multiple concerned in this primary switch is recorded by the fired condition of'the relevant one of the SITb tubes. With the inhibition referred to removed, signals are applied from the cathodes of these fired tr bes, over the respective a, b and'c leads, to, terminals A1, B1 and C1 respectively theicoupledmagnets being connected in parallel as shown, they could be connected in series. i T

Itfislto be understood that whereas each of the tubes DTS/A, STPb/c "and STTb/cin Figs.2a-2c 'hasbeen considered. as beingtypical of, a group of such tubes gwhich in each case:togethericonstitute an electronic store, the groups thus typified could possibly be replaced by multi-cathode tubes which, since each group-comprises ten tubes, could conveniently be Dekatro'ns. Thus in generaliitmay besaid that' each electronic store compri'ses'discharge tube means providing an appropriate number of electron discharge paths one or another of which T is selectively activated in accordance with the information-to bestored. What I clairnis:

l. A selective switching system including first and second eross-bar switching stages of which thefirst includesat least one and the 'secondincludes more than one "crossbar switch comprising. interconnectible horizona tal and vertical multiples transverse to each other, and

arch" having anoperating magnet associated therewith, inter-stage trunks connected between multiples in the first and'secorid stages respectively, a control circuit for first stage capable'of' selecting a free-inter-stage trunk arran'ged'to transmit to the second stage a setting signal identifying the'particular switch in the latter stage to the selected trunk is connected, a control circuit for thesecond stage responsive to receipt of said setting signal toselect an available connection through the stage,

:(Fig. 3). These signals take the form of relatively positive potentials due to the raised cathode potentials of the fired tubes The signals, at terminals A1 and clprovide anode potential for. the tube VTl via the coupled select magnets H1 of switches P1 and S1 and via the hold magnet V1 of switch P1, respectively. The signal at terminal B1 therefore causes tube VT1 to energising current through these magnets.

The independent action of a frame control, circuit in stage C will energise as previously explained the vertical magnet which relates in switch S1 to the vertical multiple to which the selected trunk is connected. The energised magnets H1 and V1 of switch P1 act in conj nction to close the contacts at the corresponding cross-point in the switch P1 and thereby establish through that switch a connection between the selected linl; and the'selected trunk to stage A} Likewise the energised magnet H1 of switch S1 acts in conjunction with the energised hold mag: net in that switch to establish throngh the switch a connection betweentheselected link and the selected trunk fire and draw said through-connection including in the last-mentioned switchamultiple transverse to that to which the selected trunlcis connected, means in the control circuit of the first stage for ellecting in accordance with the selection the contemporaneous energization of the operl in magnets associated respectively with the multiples to which opposite ends of the trunk are connected in the first stage and in said switch of the second stage, these operating magnets being electrically coupled together for .such contemporaneous energisation, and means in the from stage C. I A connection is thereby established through he of- 1 .1 n U I Whe the switches have been thus set, a holding earth is extended over thc P- wiresof the interconnected links and trunks. As indicated in Figs.'2a2c, this holding earth is applied to holding windings on the hold magnets such as HSA, HPB, HSB and HPC associated with control circuit for the second stage for efiecting in accordance with the selected through-connection the energisation of the operatingmagnet associated with the said transverse multiple included in the through-connection.

2. A selective switching system as claimed in claim 1 wherein the, inter-stage trunks are connected between frriultiples of like character in the two stages, the coupled operating magnets respectively associated with thermaltiples to which the opposite ends of each trunk are "connected being in consequence also of like character.

A selective switching system including firstand seeond 1cross bar switching stages of which the first inciudes at least one and the second includes more than onecross-bar' switch comprising interconnectible hori; ntaljand vertical multiples each having an operating magnet "associated therewith, inter-stage trunk connected between vertical multiples in the first and second stages respectively, a control circuit for the first stage capable of selecting a free inter-stage trunk and arranged to transmit to the second stage a setting signal identifying the particular switch in the latter stage vlto which the selected trunk is connected, a control circuit for the second stage responsive to receipt of said setting signal to through-connection including a horizontal multiple in,

the last-mentioned switch, means in the control circuit for the first stage for effecting in accordance with the trunk selection the contemporaneous energisation of the operating magnets associated respectively with the vertical multiple to which the opposite ends of the trunk are connected in the first stage and in said switch of the second stage, these operating magnets being electrically coupled together for such contemporaneous energisation, and means permitting in the control circuit for the second stage for effecting in accordance with the selected through-connection, the energisation of the operating magnet associated with the said horizontal multiple included in the through-connection.

4. A selective switching system including first and second switching stages constituted by cross-bar switches each having interconnectible horizontal and vertical multiples associated with respective operating magnets,-interstage trunks connected between vertical multiples in the first and second stages respectively, the second stage comprising a plurality of secondary cross-bar switches to which said trunks are connected and a plurality oftprimary switches inter-linked with the secondary switches on their horizontal multiples, a control circuit for the first stage capable of selecting a free inter-stage trunk and arranged to transmit to the second stage a setting signal identifying the particular switch in the latter stage to which the selected trunk is connected, a control circuit for the second stage responsive to receipt of said setting signal to select an available connection through the stage, said through-connection including an available link between the last-rnentioned switch and one of the primary switches in the second stage, and also an available vertical multiple in that primary switch, means in the control circuit for the first stage for effecting in accordance with the trunk selection the energisation of the operating magnet associated with the vertical multiple to which the trunk is connected in the identified switch in the second stage said operating magnet being electrically coupled to, and thereby contemporaneously energisable with, the operating magnet associated with the vertical multiple to which the other end of the trunk is connected in the first stage, andmeans in the control circuit for the second stage for effecting in accordance with the through-connection selected thereby in its stage, the energisation of the operating magnets respectively associated with the horizontal multiples to which the link included in said through-connection is connected in the primary and secondary switches and with the vertical multiple also included in the through-connection.

5. A selective switching system as claimed'in claim 4 wherein as regards each link between the primary and secondary switches of the second stage the operating magnets associated with the horizontal multiples between which such link is connected are electrically coupled together for contemporaneous energisation.

6. A selective switching system as claimed in claim 1 including an electronic store comprising electronic discharge tube means providing a plurality of discharge paths individually and respectively relating to the switches of said second stage and arranged for selective activation by the control circuit of the first stage in accordance with the particular second stage switch at which a selected to identify said particular second stage switch by the particular signal lead thus marked.

7. A selective switching system as claimed in claim 6 including also a plurality of marking paths relating individually and respectively to possible through-connections in the second stage, means for extending a signal lead marking as a marking over each of said marking paths that relates to an available through-connection by way of the switch to which the selected trunk is connected in the second stage, and one-only selection means responsive to markings thus extended over said paths to select one of them and thereby effectively select a particular available through-connection.

. 8. A selective switching system as claimed in claim 4 including a first electronic store Comprising electronic discharge tube means providing a plurality of discharge paths individually and respectively relating to the switches of said second stage and arranged for selective activation by the control circuit of the first stage in accordance with the particular second stage switch at which a selected inter-stage trunk terminates, signal leads associated with the respective discharge'paths so as'to be marked when the relevant pathis activated, said signal leads extending to the control circuit ofthe second stage to identify said particular second stage switch by the particular signal lead thus marked, a plurality of marking paths relating individually and respectively to the links between the inter-stage trunk terminates, together with signal leads associated with the respective discharge paths so as to be marked when the relevant path is activated, said signal leads extending to the control circuit of the second stage primary and secondary switches in the second stage, means for effectively extending a signal lead marking as a marking over each of said marking paths that relates to an available link connected to the secondary switch to which the selected trunk is connected, first one-only selection means responsive to markings thus extended over the marking paths to select one of them and thereby effectively select one of the last-mentioned links, a second electronic store for recording the identity of the primary switch to which the selected link is connected, this second store comprising electron discharge tube means providing a plurality of discharge paths individually and respectively relating to the primary switches of the second stage and arranged for selective activation according to the switch identity to be recorded, output leads associated with the discharge paths of the second electronic store so as to be marked when the relevant discharge path is activated, further marking paths relating individually and respectively to the vertical multiples in the primary switches, means for extending an output lead marking as a marking over each or said further marking paths that relates to an available vertical multiple in the primary switch to which the selected link is connected, second one-only selection means responsive, to markings thus extended over the furthermarking paths to select one of them and thereby select a particular one of said vertical multiples, a third electronic store for recording the identity of the selected vertical multiple in its switch, means governed by the first and second stores for effecting energisation of the operating magnets associated with the horizontal multiples between which the selected link is connected, and means governed by the second and third stores for effecting energisation of the operating magnet associated with the selected vertical multiple in the primary switch to which said link is connected.

References Cited in the file of this patent UNITED STATES PATENTS Oberman Nov. 19, 1957 

